1. Field of the Invention
The present invention relates to rotary expansion tools for expanding tubing. In particular, but not exclusively, the present invention relates to an improved expansion member for a rotary expansion tool.
2. Description of the Related Art
A number of different tools have been proposed for carrying out expansion of downhole tubing such as expandable bore-lining tubing and expandable sand screens. Applicant's International Patent Application Publication No WO 2000/37766, the disclosure of which is incorporated herein by reference in its entirety, discloses a rotary expansion tool including a number of expansion members in the form of rollers mounted on radially moveable pistons. Fluid pressure urges the pistons radially outwardly to bring the rollers into contact with the tubing to be expanded. The tool is then rotated and advanced axially through the tubing to expand the tubing to a greater internal diameter.
The rollers are compliant such that if the tool encounters a portion of tubing which cannot be expanded, the rollers can move inwardly to advance through the restriction.
Failure of conventional compliant rotary expansion tools can be accelerated by exposure of tool bearing surfaces to well materials such as drilling fluid, mud, debris and solids. Furthermore, the use of an unlubricated bearing system restricts the combination of bearing pressure and velocity which can be withstood without degradation and thermal damage.
Applicant's WO 2003/055616, the disclosure of which is incorporated herein by reference in its entirety, discloses a rotary expansion tool in which a bearing area between an expansion roller and a supporting spindle is supplied with lubrication from a sealed lubrication system.